A need exists for a hospital gown, instrument wrap or like product that is water and solvent repellent, kills bacteria but is itself non-toxic, that provides permanent antimicrobial capacity yet the antimicrobial agent itself is not extracted from the fabric in use, and that maintains its microbiocidal and repellency effectiveness over a period of time but is not inhibited by sterilization, storage or handling.
A particularly useful antimicrobial agent is DC-Q9-5700 available from Dow Corning Corporation of Midland, Mich. The material is a silicone quaternary amine, chemically 3-(trimethoxysilyl)propyloctadecyl dimethyl ammonium chloride, and is typically supplied in a 42% solids solution in methanol. This material has been used to protect textiles and inhibit odor-causing bacteria and fungi which contamination may result in odor problems, discoloration and deterioration of these textiles. Application of this type of silicone quaternary amine onto the surface of textiles has been found to inhibit the growth of microorganisms and to aid in the control of the above-mentioned problems. As such it is authorized by the Environmental Protection Agency of the United States Government for use on textile surfaces (EPA No. 34292-1) and it has also been accepted by the Food and Drug Administration of the U.S. Government for use in medical devices for use association with humans and animals.
Surgical drapes, hospital gowns, instrument wraps and like materials are typically made of non-woven textiles or other non-woven type materials. When such silicone quaternary amines are applied to a non-woven substrate it was found that the substrate was rendered partially hydrophobic, but not sufficient to repel body fluids, alcohol and like liquids typically present in a hospital environment.
The requirements for a successful medical fabric or substrate include the following:
1. Bioactivity--the substrate must be bioactive, that is it must achieve a 95% or better bactericidal effect within one hour. In other words, the material is bacteriocidal and not merely bacteriostatic as is the case with the treated wearing apparel discussed above.
2. Non-leachability--the bioactive/bactericidal material must remain on the substrate and not be leached from the substrate, but if leaching occurs it must be virtually undetectable, i.e. only less than 0.2 parts per million (0.2 ppm) from a 6 inch.times.6 inch swatch according to test procedures, described in more detail below. Non-leachability or substantial nonleachability is a factor of the fabric sample or swatch size being tested.
3. International Nonwovens and Disposables Association--The fabric must be water repellent as measured by (INDA) test IST 80.7-70 (R77), referred to herein as the mason jar test. In this test a swatch of sample fabric is placed over the mouth of a mason jar containing sufficient normal saline (0.9% NaCl) that when the jar is inverted a 4.5" head of water results. The top ring is screwed onto the jar, the jar is inverted and placed on a glass plate. The inverted jar is observed and the time is measured until the jar leaks. The minimum time for a successful sample is 30 minutes for an instrument wrap fabric, and 45 minutes for a hospital gown fabric. In any event, an average time for successful fabrics is at least one hour after which the test is stopped.
4. Spray rating, a measure of water repellency--the subject fabric should be rated to have a minimum value of 75 according to the American Association of Textile Chemists and Colorists (AATCC) spray rating test 22-1971. In this test the fabric is held tightly on a metal hoop and sprayed with 250 ml. of water. The fabric is then rated by comparison of the sprayed fabric with pictures on a standard chart.
5. Alcohol repellency--is measured in a test in the manner of INDA test IST 80.9-74 (R77) which uses ethanol wherein for my comparisons and measurements isopropanol was the alcohol that was used. In this test equal amounts of serially diluted isopropanol solutions, ranging from 60% to 100% in increments of 10 percent, are placed on a sample fabric arranged on a flat surface such as a laboratory counter top. After five minutes the surface is usually inspected and the highest concentration retained by the sample fabric is noted. The minimum value is a 70% isopropanol solution, i.e. a 70% isopropanol solution is retained by the fabric but the 80% solution penetrates through the fabric to the underlying surface. The minimum value is 70%; fabrics according to my invention typically retain 80% and 90% isopropanol solutions.
6. Static decay--this is a measure of dissipation of static electricity from the fabric and is required in surgical environments where combustible gases are present. Static decay is measured according to NFPA test 56A in which a test fabric is placed in a meter (model 406B, Electro-Tech Systems) and charged to 5,000 volts DC. The meter measures the time, in seconds, required to deplete to 10% of the original charge or 500 volts DC; minimum values for this test are about 0.5 seconds, although preferred values are less than 0.2 seconds.
7. Cytotoxicity--the leachate removed from a sample of the medical substrate must not exhibit cytotoxicity to cells. This includes not only the antimicrobial agent itself but also other finishes, colorants or the like that may also be applied to the substrate. A typical testing procedure includes adding a standardized cell culture to a leachate recovered from a predetermined sample size of the substrate being tested, incubating the culture plus leachate and observing the culture for either cell death or morphological change to the cells in the culture.
8. The medical substrate must be non-flammable in accordance with standard CS-191-53.
9. Fastness--Although not required for certain end uses, if a dye is applied it must stay on the substrate and be fixed thereto thus free from crocking and water bleeding.